(1) Field of the Invention
The present invention relates to a microtome for cutting e.g. a brain specimen into thin slices for use in physiological experiments.
(2) Description of the Related Art
One example of a conventional microtome is disclosed in Publication of Examined Japanese Patent Application No. SHO 58(1983)-29453. The microtome disclosed therein has a stage onto which a specimen is fixedly placed and a base driven by a motor to slide relatively to the stage. The base is provided with a movable body that oscillates in a direction perpendicular (side-to-side direction) to the sliding direction. The movable body is provided with a cutting blade attached thereto, and with another motor mounted on the base. The rotational movements produced by said another motor are converted by a crank mechanism into horizontal movements to oscillate the movable body, i.e. the cutting blade in the horizontal direction. Wile oscillating, the cutting blade is moved forward by the slide thereby cutting a thin slice from the specimen.
A conventional microtome as above works well while it is new, but eventually causes a problem with a dovetailed recess provided in the base that is in fit with a dovetail tenon protruded from the movable body. To be more specific, through the use over a long period of time, the dovetailed recess wears out, thereby producing an undesirable play. Due to the play, the fit between a rotation shaft and a coupler constituting the crank mechanism becomes poor. Such poor fit causes the cutting blade to wobble horizontally (oscillation in the horizontal direction) As a result, the cutting blade ends up smashing the specimen from above thereby killing cells present in the specimen. This is a problem especially in brain physiology experiments as whether cells in a specimen used are dead or alive greatly matters in the study.
In view of the above problems, an object of the present invention is to provide a microtome that is free from horizontal wobbling of a cutting blade even after a long period of use, so that thin slices of a specimen are obtained in good condition with the cells remain alive.
Another object of the present invention is to provide a microtome capable of oscillating only in a desired direction while suppressing oscillation in other directions.
Yet another object of the present invention is to provide a microtome of which cutting blade oscillates to achieve sharp cutting, i.e., swings quickly from side to side making a click-like motion between each swing.
Yet another object of the present invention is to provide a microtome capable of suppressing the judder that may occur at a mechanical resonance when the oscillation frequency is made to vary.
Yet another object of the present invention is to provide a microtome of which oscillation amplitude and frequency are adjustable, so that a specimen is optimally cut depending on the type or the state of the specimen.
To achieve the above stated objects, a microtome according to the present invention includes: a stage for fixedly placing the specimen thereon; a base arranged slidably relative to the stage; a movable body arranged to oscillate in a direction perpendicular to a direction in which the base slides; a cutting blade for cutting the specimen placed on the stage, the cutting blade being attached to the movable body at a forward part with respect to the sliding direction; a plurality of resilient couplers coupling the movable body to the base so as to allow for the oscillation; a first magnet made of an electromagnet and mounted on one of the base and the movable body; a control circuit for supplying an alternating signal to the first magnet; and a second magnet mounted on the other of the base and the movable body in opposed relation to the first magnet. The second magnet reacts to attraction and repulsion that is alternately resulting from an alternating field generated by the first magnet, so that the movable body is displaced against resilience of the resilient couplers in the direction perpendicular to the sliding direction, whereby the cutting blade oscillates. By sliding the base forward relative to the stage, the cutting blade cuts into the specimen with oscillation so that the thin slice is cut from the specimen.
Here, the plurality of resilient couplers maybe arranged in a pair. Each resilient coupler may be made up of a plurality of spring plates overlapped in layers. The pair of resilient couplers may be attached to the base with a first end of each resilient coupler being fixed to the base at two separate locations, and a second end of each resilient coupler being fixed to the movable body at lateral sides.
Here, the second magnet may be a permanent magnet. The second magnet may be different from the first magnet in magnetic pole distance. The first magnet may generate, when energized, magnetic force attracting the second magnet in a direction where unlike polarities are adjacent to each other owing to the different magnetic pole distance.
Further, the first magnet may be fixed to the base. The second magnet may be made of a permanent magnet magnetized to have a north pole and a south pole at respective ends thereof. The permanent magnet may be fixed to the movable body with the north pole and the south pole opposing to a pair of legs of a core of the first magnet.
Here, the microtome may further include: a detector for detecting a magnitude of a current passing through the first magnet; and a current control circuit for controlling the current passing through the first magnet so that the detector detects a constant magnitude.
Here, the microtome may further include an operating unit for variably controlling an amplitude and a frequency of the current passing through the first magnet.
With the above construction, the microtome includes the cutting blade for slicing a specimen, and the cutting blade is attached to the movable body that is coupled to the base with the resilient couplers. The blade is made to oscillate through the use of the driving electromagnet and the magnet on the principles of a linear motor. Thus, the microtome operates without deterioration even after a long period of use, and is capable of cutting the specimen without killing the cells present in the specimen. Further, since the blade oscillates with the use of the electromagnet and the magnet in combination, the movable body oscillates more powerfully.
Still further, since each resilient coupler is made of a plurality of spring plates overlapped in layers, the movable body is allowed to oscillate only in the fixed direction.
Still further, the permanent magnet mounted on the movable body is magnetized in the thickness direction, so that each side of the magnet has unlike polarity from each other. This arrangement helps the movable body to oscillate more powerfully. Consequently, the blade cuts a specimen more sharply.
Still further, the presence of feedback circuit serves to suppress the judder that may occur at mechanical resonance when the oscillation frequency is made to vary.
Still further, since the frequency and the amplitude of oscillation of the blade is variable in a continuous manner, adjustment maybe made to achieve an optimal cutting of a specimen depending on the stiffness or other properties of the specimen.